As the integration density of semiconductor devices has increased, the width of patterns formed on a semiconductor substrate and an interval between the patterns have been decreased. Formation of photomasks is indispensable when manufacturing semiconductor devices. The photomask includes a mask pattern defining a variety of elements. The size of the mask patterns continue to get smaller to provide smaller, highly integrated devices. Since a high-quality photomask is difficult to obtain and manufacturing costs of the photomask continue to increase, it may be important to obtain the high-quality photomask early in view of the photomask manufacturing cost and a turn-around time (TAT) reduction.
When the size of the mask pattern gets so small as to reach resolution limit of the exposure tool, it is difficult to transfer on the electronic device substrate a pattern of the same shape and CD that correspond to the mask pattern formed on the photomask due to an optical proximity effect. In order to form a high-resolution pattern with a linewidth smaller than the wavelength of light, an optical proximity correction (OPC) technique for correcting the shape of the photomask beforehand is used in consideration of deformation of a pattern formed on a wafer due to the optical proximity effect.
Recently, a design rule has continuously decreased in order to improve the performance of transistors and produce more chips with respect to net die standard. With the shrinkage of the linewidth of gate patterns, the dependence of the linewidth of the gate patterns on the dimension of a space between adjacent gate patterns becomes strongly marked, so that it becomes difficult to control the linewidth of the gate patterns. Accordingly, it mat be very important to elevate the accuracy of a photomask in order to satisfy a strict target value of an after development inspection (ADI) critical dimension (CD). Also, it becomes stricter to control a mask mean-to-target (MTT) and CD uniformity.
Furthermore, the so-called “peanuts” effect occurs due to the optical proximity effect so that an outer portion of a pattern is curved, and patterns having shapes that cannot ensure an MTT using conventional one-dimensional measurement methods are increasing. To address these problems, a method of measuring the area of a pattern has been proposed. However, it may be necessary to develop a method of converting the measured area of the pattern into conventional one-dimensional MTT.